1. Field
The present embodiments generally relate to methods for adjusting yields in olefin production. More particularly, embodiments of the present invention relate to methods for adjusting yields from high severity fluid catalytic cracking units.
2. Description of the Related Art
Olefins, which have long been desired as products in the petrochemical industry, have been used as feedstocks to produce a wide variety of finished products such as polyethylene, polypropylene, other polymers, alcohols, vinyl chloride monomer, and other petrochemicals. Olefins typically are produced by cracking longer molecular weight hydrocarbons found in crude oil, such as olefinic naphtha. Olefinic naphtha contains saturated, olefinic, and aromatic hydrocarbons in the C4 to C10 range. The majority of aromatics in the hydrocarbon feed are not converted in a cracking process, such as fluid catalytic cracking (“FCC”), which limits the production of desired products, such as linear olefins.
Standard solvents have been used to remove aromatics from the cracked hydrocarbons. Such solvents require saturating the olefins with hydrogen prior to removing the aromatics because the olefins are also soluble in the solvent. Thus, solvent extraction while effectively removing the undesirable aromatic compounds, also removes the desirable olefins, severely limiting product yield. Various extraction techniques have been used for specialized olefinic extractions as exemplified by U.S. Pat. Nos. 4,267,034 and 7,019,188. Research into the use of dimethyl sulfoxide as a solvent for the extraction of aromatics from mixed hydrocarbon streams is exemplified by: E. I. Shcherbina, et al., Extractive Recovery of Aromatic Hydrocarbons from Pyronapthas with Dimethyl Sulfoxide, translated from Khimiya i Tekhnologiya Topliv i Masel No. 6 pp. 13-16 (June, 1973).
There is a need, therefore, for a method for selectively removing aromatics from olefinic naphtha without removing or chemically altering the olefins present, thereby increasing olefin production.